JP2004023892A - Inverter device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an inverter device in which a speed feedback value can be matched to a speed command value in the case of leading in a drive by the inverter device and an overcurrent can be suppressed. <P>SOLUTION: The inverter device includes two or more sets of rectifier circuits 16, 17 each for converting an AC power to be input via a multi-winding transformer 4 into a DC power and inverter circuits 18, 19 connected to DC output terminals of the rectifier circuits 16, 17 in which the DC output terminals side are connected in series with each other; and DC reactors 20, 21 inserted between the rectifier circuits and inverter circuits in which the AC power output terminals are multiplexed by an output multi-winding transformer 6 to drive a motor 8 after starting by compensating. The inverter device includes a speed gradient signal generator 39 for generating a speed gradient signal. The inverter device controls the motor 8 with the speed feedback value calculated based on a detected value obtained by detecting the voltage supplied to the motor 8 by a transformer 26 as a speed reference value of the speed gradient signal generator 39 until the speed reference signal is input at a starting time. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a current source inverter device used for speed control of an AC motor.
[0002]
[Prior art]
FIG. 11 shows, for example, Mitsubishi Electric Technical Report, Ve 1.61, No. FIG. 10 is a system configuration diagram of the conventional device shown in FIGS. 10 and 1987 (P48 to P53). 11, 1 is a commercial AC power supply for a main circuit, 2 is a commercial AC power supply for a field device, 3 is a circuit breaker, 4 is an input multi-winding transformer, 5 is an inverter device, and 6 is an output multi-winding transformer. , 7 are circuit breakers, 8 is an AC motor driven by the inverter device 5, 9, 10, 11, and 12 are circuit breakers, 13, 14, and 15 are starting reactors, and 16 and 17 are forward conversion circuits using thyristors. , 18 and 19 are inverse conversion circuits using thyristors, 20 and 21 are smoothing reactors, and 22 is a field thyristor power supply.
[0003]
Reference numerals 23 and 24 denote main circuit current detection CTs, 25 a field current detection CT, 26 a PT for detecting the voltage of the electric motor 8, 27 an external speed command generator, and 28 a A contact which is turned on in response to an external operation command signal, 29 is a voltage detector for detecting the motor voltage detected by the PT 26, 30 is a phase detector for detecting the phase from the voltage signal output of the voltage detector 29, 31 is a voltage The speed detector calculates the speed from the voltage signal output of the detector 29.
[0004]
A speed controller 32 compares and controls a speed reference signal from an external speed command generator 27 and a speed feedback signal output from the speed detector 31, and 33 denotes a current command output from the speed controller 32. And a main circuit current feedback value detected by the main circuit current sensors 23 and 24. The converter controller controls the current of the converter and transmits and controls the thyristor gate signal of the forward conversion circuits 16 and 17 using thyristors. is there.
[0005]
Further, 34 is a vector calculator for calculating the control angle of the inverter from the voltage, current, speed feedback value and current command value, and 35 is a control angle β reference from the vector calculator, the speed feedback value and the phase detector 30. An inverter controller 36 for transmitting and controlling the thyristor gate signal of the forward conversion circuits 18 and 19 using a thyristor based on the detected phase, a field current reference calculated by a vector calculator 34 and a current sensor 25 A field controller 37 that compares the field current feedback value and controls the field thyristor device 22 is a controller for the inverter.
[0006]
Next, the operation will be described. In the system in which the high-voltage AC motor 8 is multiplexed and boosted by the output transformer 6 to control the activation of the high-voltage AC motor 8, when the AC motor 8 to be driven by the inverter device 5 is a synchronous motor, the frequency at which the inverter device 5 starts from 0 Oscillation may occur and the output transformer 6 may saturate, and starting from zero speed is not possible.
[0007]
Therefore, after the AC motor 8 is accelerated by starting the compens by the starting reactors 13, 14, 15 and the circuit breakers 9, 10, 11, 12, for example, the time at which the speed becomes about 10% is reduced by the acceleration torque and the load torque of the motor. The circuit breakers 9, 10, 11, and 12 of the starting reactors 13, 14, and 15 are opened by a timer relay (not shown), and the circuit breaker 7 provided between the output transformer 6 and the motor 8 is calculated. throw into. The contact 28 is turned on by an operation command signal from the outside of the inverter device 5 linked to the closing completion signal of the circuit breaker 7, and driving of the AC motor 8 by the inverter device 5 is started.
[0008]
In that case, the electric motor 8 is rotating in a free-run state. If the load (not shown) of the electric motor 8 is a fan, its inertia is large and the speed does not decrease much during the operation time of the circuit breaker or the like. The inverter device 5 performs speed control based on a speed reference value (speed command value) from an external speed command generator 27. When the inverter is started, the external speed command generator 27 moves from the assumed pull-in speed, for example, the assumed 10% speed, to the normal operating speed reference in a normally inclined manner.
[0009]
The speed controller 32 calculates a speed reference value which is an output of the speed command generator 27 and a speed feedback value calculated by the speed detector 31 from a voltage signal of the PT 26 for measuring the voltage of the electric motor 8 and a voltage signal of the voltage sensor 29. Compare and output a current reference signal according to the deviation. The magnitude of the current flowing through the AC motor 8 is controlled by the phase control of the converter in accordance with a command from the converter controller 33 based on the current reference signal. Therefore, the difference between the speed reference value and the speed feedback value is the magnitude of the current, and the larger the difference is, the larger the current flows.
[0010]
[Problems to be solved by the invention]
Since the conventional inverter device is configured as described above, when switching from driving the compensator by the reactors 13, 14, 15 of the AC motor 8 to driving by the inverter device 5, the consistency between the actual speed and the speed reference is: Due to the timer relay time calculated on the desk, the actual speed deviation may be large, but if the motor load has a large inertia like a fan, the deviation does not occur much and the current does not increase much . However, when the load of the motor 8 is a load with a relatively low inertia such as a pump or a compressor, the speed drop during free-run is fast, and the deviation between the speed reference signal and the speed feedback may increase. There was a problem that an excessive current sometimes flowed.
[0011]
The present invention has been made to solve the above-described problems, and an inverter device that can match a speed feedback value and a speed command value when drawing in drive by the inverter device and that can suppress overcurrent is provided. With the goal.
[0012]
[Means for Solving the Problems]
An inverter device according to the present invention includes a forward conversion circuit that converts AC power input through an input multi-winding transformer into DC power, and is turned on by a drive control signal connected to a DC output terminal of the forward conversion circuit. A series circuit composed of two or more electric switches whose periods are controlled in series is connected in parallel for a predetermined number of phases, and has two or more sets of inversion circuits that output AC power from the midpoint of each series circuit, Each DC output terminal side is connected in series, consists of a DC reactor inserted between the forward conversion circuit and the reverse conversion circuit, the AC power output end of which is multiplexed by the output multi-winding transformer, and after the start of compen The inverter device for driving the electric motor has a speed gradient signal generator for generating a speed gradient signal in which the speed reference signal is ramped according to the set gradient. Is characterized in that to control the speed feedback value is calculated based on the voltage supplied to the electric motor to the detected value detected by the transformer as a speed reference value of the speed gradient signal generator.
[0013]
Further, a minimum speed command setting device 48 for giving an initial speed reference value to the speed gradient signal generator is provided, and the minimum speed command setting value of the minimum speed command setting device is set until the speed reference signal is input at startup. A value equal to the speed feedback value is set, and a minimum speed command set value equal to the speed feedback value is given to the speed gradient signal generator as an initial speed reference value.
[0014]
Further, the control unit controls the speed feedback value as a speed reference value of the speed gradient signal generator until a speed reference signal is input at the time of startup, and bypasses the speed gradient signal generator during continuous operation to control a speed reference signal from outside. Characterized in that a contact for switching to control the speed based on the contact is provided.
[0015]
Further, the control unit controls the speed feedback value as a speed reference value of the speed gradient signal generator until a speed reference signal is input at the time of startup, and bypasses the speed gradient signal generator during continuous operation to control a speed reference signal from outside. Characterized in that a contact for switching to control the speed based on the contact is provided.
[0016]
Also, a resistor for limiting an exciting current is connected in series to the primary side of the transformer.
[0017]
Further, the present invention is characterized in that the speed feedback value is calculated using a pulse encoder that detects a rotation speed of the electric motor instead of the transformer.
[0018]
Further, the invention is characterized in that the speed feedback value is calculated using a resolver that detects a rotation speed of the electric motor, instead of the transformer.
[0019]
Further, the invention is characterized in that the speed feedback value is calculated using a mechanical distributor connected to the electric motor instead of the transformer.
[0020]
Further, the present invention is characterized in that the serial output terminals of the forward conversion circuit and the inverse conversion circuit are not connected in series, but are independent parallel circuits.
[0021]
Further, the forward conversion circuit and the inverse conversion circuit are constituted by a set of main circuits.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1 FIG.
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In FIG. 1, the same parts as those of the conventional example shown in FIG. 11 are denoted by the same reference numerals, and description thereof will be omitted. As a new code, 38 is a contact that is turned on by an operation command signal from outside the inverter device 46, 39 is a speed gradient signal generator, and 40 switches the input signal of the speed gradient signal generator 39 in conjunction with the contact 38. A contact drive circuit for operating the contacts 41 and 42; 43, a ramp time setter for setting the ramp time (gradient) of the velocity ramp signal generator 39; 44, a minimum set value of the output of the velocity ramp signal generator 39; A setting device 45 is an inverter control device of the present invention, and 46 is an inverter device equipped with the inverter control device 45 of the present invention.
[0023]
Next, the operation will be described. When the electric motor 8 is started by the starting reactors 13, 14, and 15 and is switched to the drive by the inverter device 46, the contact 41 remains in contact drive until the operation command contact 38 of the inverter device 46 is turned on by an external command (not shown). It is turned ON by the circuit 40. The speed gradient signal generator 39 outputs an output signal such that the input signal and the output signal become equal at the gradient set by the gradient time setting unit 43, and becomes constant when the input signal and the output signal become equal. Therefore, the output of the speed inclination signal generator 39 matches the speed feedback value calculated by the speed detector 31 until the operation command contact 38 of the inverter device 46 is turned on.
[0024]
When the operation command contact 38 is turned on, the contact 41 is turned off and the contact 42 is turned on by the contact drive circuit 40, and the input signal of the speed gradient signal generator 39 is changed from the speed feedback value to the speed reference of the speed command generator 27 from the outside. It switches to the value (speed command value) and follows the reference value. In this case, as the speed command value of the speed controller 32 at the time of starting, a value equal to the value of the speed feedback value is given from the speed inclination signal generator 39. In order to prevent saturation of the output transformer 6, a minimum speed command value is given from the setting device 44 to the speed gradient signal generator 39.
[0025]
Therefore, in the first embodiment, the speed reference value at the start of the inverter device input to the speed gradient signal generator 39 is set to be equal to the speed feedback value. There is no deviation from this, and it is possible to prevent the occurrence of overcurrent when driving and drawing the motor 8 in the free-run state by the inverter device 46, and to obtain a highly reliable device.
[0026]
Embodiment 2 FIG.
In the first embodiment, the case where the input signal of the speed gradient signal generator 39 is matched with the speed feedback value by the contact drive circuit 40 has been described. However, as shown in FIG. A speed feedback value is given to the minimum speed command setting device 48 via a contact 47 which is turned off simultaneously with the ON signal of the operation command contact 28 of the inverter or after a set time of the timer so as to be equal to the value. The minimum speed command set value of 48 is set to a value equal to the speed feedback value of the motor 8 at the time of starting the inverter, and the minimum speed command set value equal to the speed feedback value is supplied to the speed gradient signal generator 39 as an initial speed reference value. By doing so, it is possible to simplify the circuit configuration, suppress the overcurrent at the time of start-up by the inverter device 50, and perform an operation input from outside (not shown). To decree 28 can follow the beginning of startup to the speed command value of the external velocity command generator 27 without delay operation.
[0027]
Embodiment 3 FIG.
In the first embodiment, the case where the input signal of the speed gradient signal generator 39 is matched with the speed feedback value by the contact drive circuit 40 has been described. However, as shown in FIG. Is switched between the path by the speed gradient signal generator 39 and the path directly provided by the speed command generator 27 by the contacts 51 and 52, so that the speed reference from the speed gradient signal generator 39 is only obtained when the inverter is started. A value is given to the speed controller 32 to suppress an overcurrent at the time of starting by the inverter device 54, and by switching to a normal operation state by the contact 51 and the contact 52 according to a switching command input from the outside (not shown), By giving the speed reference value from the command generator 27 to the speed controller 32, the delay of the inclination time with respect to the speed reference signal of the external speed command generator 27 is reduced. Ku can follow. In other words, the speed feedback value is controlled as the speed reference value of the speed gradient signal generator 39 until the speed reference signal is input at the time of startup, and the speed gradient signal generator 39 is bypassed during continuous operation to provide an external speed reference signal. By switching to perform speed control based on this, it is possible to follow the speed reference signal of the external speed command generator 27 without delay of the inclination time.
[0028]
Embodiment 4 FIG.
In the second embodiment, the case has been described where the minimum speed command value given to the speed gradient signal generator 39 is matched with the speed feedback value given from the setter 48. However, as shown in FIG. By switching between a path provided by the speed gradient signal generator 39 and a path directly provided by the external speed command generator 27 by the contacts 55 and 56, the speed gradient signal generator is provided only when the inverter is started. The speed reference value from 39 is supplied to the speed controller 32 to suppress the overcurrent at the time of starting by the inverter device 54, and to switch to the normal operation state by the contact 55 and the contact 56 according to a switching command input from outside (not shown). Thus, it is possible to follow the speed command value of the external speed command generator 27 without delay of the inclination time. The operation circuit can be simplified by turning off the input of the speed feedback value to the minimum speed command setting device 48 at the contact 56.
[0029]
Embodiment 5 FIG.
In the first, second, third and fourth embodiments, the case where the input of the voltage detector 29 is given from the PT 26 has been described. However, as shown in FIG. 5, the excitation current of the PT 60 is suppressed in series with the primary side of the PT 60. By connecting the resistor 59, it is possible to use the PT60 compatible with commercial power without the need for a special PT26 that does not saturate at low frequencies, and to set the lower limit condition of the operation pull-in frequency by the inverter device 62. An inverter control device 61 that can be reduced in cost and that is economically excellent can be obtained.
[0030]
Embodiment 6 FIG.
In the first, second, third, fourth and fifth embodiments, the case where the speed feedback value is obtained by calculating the voltage signal of the voltage detector 29 by the speed detector 31 has been described. However, as shown in FIG. Then, a pulse encoder (PLG) 63 is used as a speed detector, the speed is calculated from the signal of the PLG 63 by the speed detector 64 to obtain a speed feedback value, and the phase calculator 65 similarly outputs the phase detected from the signal of the PLG 63. As a result, it is possible to obtain the inverter control device 67 with higher accuracy as the speed feedback value. Further, the voltage detector 66 can be simplified by using only the function of the voltage feedback value.
[0031]
Embodiment 7 FIG.
In the first, second, third, fourth and fifth embodiments, the case where the speed feedback value is obtained by calculating the voltage signal of the voltage detector 29 by the speed detector 31 has been described. However, as shown in FIG. Then, a resolver 69 is used as a speed detector, the speed is calculated from the signal of the resolver 69 by the speed detector 70 to obtain a speed feedback value, and the phase calculator 65 similarly outputs the phase detected from the signal of the resolver 69. By doing so, a more accurate inverter control device 72 can be obtained as a phase detector.
[0032]
Embodiment 8 FIG.
In the first, second, third, fourth and fifth embodiments, the voltage detector 29 is used as an electric distributor, and the speed feedback value is calculated by the speed detector 31 based on the voltage signal. As shown in FIG. 8, a mechanical distributor 74 is connected to the electric motor 8, and a speed detector 75 calculates a speed from a signal of the mechanical distributor 74 to obtain a speed feedback value. By outputting the phase detected from the signal of the device 74 from the phase detector 76, a more accurate inverter control device 77 can be obtained as a thyristor firing device.
[0033]
Embodiment 9 FIG.
In the first to eighth embodiments, as a main circuit configuration, a forward conversion circuit 16 that converts AC power input to the multi-winding transformer 4 into DC power, and a connection to a DC output terminal of the forward conversion circuit 16 And a reverse conversion circuit 18 that connects two or more electric switches whose conduction period is controlled in series by a drive control signal connected in series for a predetermined number of phases, and outputs AC power from a middle point of each series circuit. , The DC output terminals are connected in series, and the DC reactor 20 is inserted between the forward conversion circuit and the inverse conversion circuit. However, as shown in FIG. Since the output terminals are not connected in series but are independent parallel circuits, the capacity can be easily increased by increasing the number of parallel circuits, and an economically excellent device can be obtained.
[0034]
Embodiment 10 FIG.
In the first to ninth embodiments, a multiplex inverter device has been described. However, as shown in FIG. 10, even in a device having a single main circuit configuration, a high-voltage motor 8 can be driven, and a device economically excellent for driving a low-voltage, large-current motor can be obtained. In FIG. 10, reference numeral 90 denotes a forward conversion circuit for converting AC power input to the transformer 89 into DC power, and reference numeral 92 is connected to the DC output terminal of the forward conversion circuit 90 and the conduction period is controlled by a drive control signal. Conversion circuit that connects two or more electrical switches in series to each other in parallel for a predetermined number of phases and outputs AC power from the middle point of each series circuit. Reference numeral 91 denotes a forward conversion circuit 90 and an inverse conversion circuit 92. An AC power output terminal of the DC reactor is stepped up by a transformer 93. 94 is a converter controller, 95 is an inverter controller, 96 is a control device, and 97 is an inverter device.
[0035]
【The invention's effect】
As described above, according to the present invention, the speed reference value at the start of the inverter device input to the speed gradient signal generator is set to be equal to the speed feedback value. There is no deviation from the value, and it is possible to prevent the occurrence of overcurrent when driving and pulling the motor in the free-run state by the inverter device, and to obtain a highly reliable device.
[0036]
Also, give a speed feedback value to the minimum speed command setting device, make the minimum speed command setting value of the minimum speed command setting device equal to the speed feedback value of the motor at the time of starting the inverter, and set the minimum speed command value equal to that speed feedback value. By giving the value to the speed gradient signal generator as the initial speed reference value, it is possible to simplify the circuit configuration, suppress overcurrent at startup by the inverter device, and generate an external speed command without operation delay. Start following start of the speed command value of the heater.
[0037]
In addition, the speed command value of the speed controller is switched between a path by the speed gradient signal generator and a path directly given from the speed command generator by a contact point. The speed reference value from the external speed command generator is given to the speed controller by controlling the overcurrent at the start by the inverter device and switching to the normal operation state by the contact. In this way, it is possible to follow the speed reference signal of the external speed command generator without delay of the inclination time.
[0038]
In addition, by switching the speed command value of the speed controller between the path by the speed gradient signal generator and the path directly given from the external speed command generator by contacts, the speed gradient signal is generated only when the inverter is started. The speed reference value from the generator is given to the speed controller to suppress the overcurrent at the time of starting by the inverter device, and by switching to the normal operation state by the contact, the inclination time with respect to the speed command value of the external speed command generator Without delay. Further, the operation circuit can be simplified by turning off the input of the speed feedback value to the minimum speed command setting device at the contact point.
[0039]
Also, by connecting an exciting current suppression resistor in series with the primary side of the transformer, a transformer compatible with commercial power is used without the need for a special transformer that does not saturate at low frequencies. Thus, the lower limit condition of the operation pull-in frequency by the inverter device can be reduced, and an economically excellent inverter control device can be obtained.
[0040]
Further, since a pulse encoder is used as the speed detector and the speed is calculated from the signal of the pulse encoder to obtain a speed feedback value, it is possible to obtain an inverter control device with higher accuracy as the speed feedback value. Further, the voltage detector can be simplified by using only the function of the voltage feedback value.
[0041]
Also, by using a resolver as a speed detector, calculating the speed from the signal of the resolver and setting it as a speed feedback value, the phase calculator similarly outputs the phase detected from the signal of the resolver, so that the phase detector Thus, a more accurate inverter control device can be obtained.
[0042]
In addition, a mechanical distributor is connected to the electric motor, the speed is calculated from the signal of the mechanical distributor by a speed detector to obtain a speed feedback value, and the phase detected from the signal of the mechanical distributor is output from the phase detector. By doing so, a more accurate inverter control device can be obtained as the thyristor ignition device.
[0043]
In addition, since the DC output terminals are not connected in series but are formed as independent parallel circuits, the capacity can be easily increased by increasing the number of parallel circuits, and an economically excellent device can be obtained.
[0044]
Furthermore, even with a single main circuit configuration, a high-voltage motor can be driven, and a device economically superior to driving a low-voltage, large-current motor can be obtained.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram showing an inverter device according to Embodiment 1 of the present invention.
FIG. 2 is a system configuration diagram showing an inverter device according to Embodiment 2 of the present invention.
FIG. 3 is a system configuration diagram showing an inverter device according to Embodiment 3 of the present invention.
FIG. 4 is a system configuration diagram showing an inverter device according to Embodiment 4 of the present invention.
FIG. 5 is a system configuration diagram showing an inverter device according to Embodiment 5 of the present invention.
FIG. 6 is a system configuration diagram showing an inverter device according to Embodiment 6 of the present invention.
FIG. 7 is a system configuration diagram showing an inverter device according to Embodiment 7 of the present invention.
FIG. 8 is a system configuration diagram showing an inverter device according to Embodiment 8 of the present invention.
FIG. 9 is a system configuration diagram showing an inverter device according to Embodiment 9 of the present invention.
FIG. 10 is a system configuration diagram showing an inverter device according to Embodiment 10 of the present invention.
FIG. 11 is a system configuration diagram showing an inverter device according to a conventional example.
It is a system configuration diagram.
[Explanation of symbols]
1 commercial AC power supply for main circuit, 2 commercial AC power supply for field device, 3 breaker, 4 input multi-winding transformer, 5 inverter device, 6 output multi-winding transformer, 7 circuit breaker, 8 AC motor, 9 , 10, 11, 12 Circuit breaker, 13, 14, 15 Starting reactor, 16, 17, 79, 82, 90 Forward conversion circuit using thyristor, 18, 19, 81, 84, 92 Reverse conversion using thyristor Circuit, 20, 21, 80, 83, 91 Smoothing reactor (DC reactor), 22 field thyristor power supply, 23, 24 CT for main circuit current detection, 25 CT for field current detection, 26 PT, 27 Speed command generator , 28 operation command contact, 29 voltage detector, 30 phase detector, 31 speed detector, 32 speed controller, 33, 85, 94 converter controller, 34 vector calculator, 35, 86, 95 b Barter controller, 36 field controller, 37 controller, 38 contacts, 39 speed gradient signal generator, 40 contact drive circuit, 43 setting device, 44 setting device, 45, 87, 96 control device, 46, 50, 54, 62 , 88, 97 Inverter device, 48 Minimum speed command setting device, 51, 52, 55, 56 contacts, 59 Excitation current suppression resistor, 60 PT, 61 Inverter control device, 63 PLG, 64 Speed detector, 65 Phase calculator, 66 voltage detector, 69 resolver, 70 speed detector, 72 inverter controller, 74 mechanical distributor, 75 speed detector, 76 phase detector, 77 inverter controller, 93 output transformer.

Claims (10)

A forward conversion circuit that converts AC power input through an input multi-winding transformer into DC power, and an electric switch whose conduction period is controlled by a drive control signal connected to a DC output terminal of the forward conversion circuit. Two or more series circuits connected in series are connected in parallel for a predetermined number of phases, and there are two or more sets of inversion circuits that output AC power from the midpoint of each series circuit, and each of the DC output terminals is connected in series. In the inverter device, which comprises a DC reactor inserted between the forward conversion circuit and the reverse conversion circuit, the AC power output end of which is multiplexed by the output multi-winding transformer, and drives the motor after the start of the compen.
A speed gradient signal generator that generates a speed gradient signal in which the speed reference signal is ramped according to a set gradient, and a voltage supplied to the motor is supplied by a transformer until the speed reference signal is input at the time of starting. An inverter device which detects and controls a speed feedback value calculated based on the detected value as a speed reference value of the speed gradient signal generator. The inverter device according to claim 1,
The speed gradient signal generator is provided with a minimum speed command setting device 48 for giving an initial speed reference value, and the minimum speed command setting value of the minimum speed command setting device is fed back to the speed feedback until a speed reference signal is input at the time of starting. An inverter device, wherein the initial value is set to a value equal to a value, and a minimum speed command set value equal to the speed feedback value is given to the speed gradient signal generator as an initial speed reference value. The inverter device according to claim 1,
The speed feedback value is controlled as a speed reference value of the speed gradient signal generator until a speed reference signal is input at the time of start-up, and during continuous operation, the speed gradient signal generator is bypassed and based on an external speed reference signal. An inverter device comprising a contact for switching for speed control. The inverter device according to claim 2,
The speed feedback value is controlled as a speed reference value of the speed gradient signal generator until a speed reference signal is input at the time of start-up, and during continuous operation, the speed gradient signal generator is bypassed and based on an external speed reference signal. An inverter device comprising a contact for switching for speed control. The inverter device according to any one of claims 1 to 4,
An inverter device, wherein a resistor for limiting an exciting current is connected in series to the primary side of the transformer. The inverter device according to any one of claims 1 to 5,
An inverter device, wherein the speed feedback value is calculated using a pulse encoder that detects a rotation speed of the electric motor instead of the transformer. The inverter device according to any one of claims 1 to 5,
An inverter device, wherein the speed feedback value is calculated using a resolver that detects a rotation speed of the electric motor instead of the transformer. The inverter device according to any one of claims 1 to 5,
An inverter device, wherein the speed feedback value is calculated using a mechanical distributor connected to the electric motor instead of the transformer. The inverter device according to any one of claims 1 to 8,
An inverter device, wherein the forward conversion circuit and the reverse conversion circuit are not connected in series to each other and are independent parallel circuits. The inverter device according to any one of claims 1 to 8,
An inverter device, wherein the forward conversion circuit and the inverse conversion circuit are constituted by a set of main circuits.

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